Expiratory obstruction in patients with Duchenne muscular dystrophy under non-invasive ventilation: A step-by-step analysis of a new obstructive pattern

Abstract

Purpose: Non-invasive ventilation (NIV) is the reference standard for managing chronic hypoventilation in patients with Duchenne muscular dystrophy (DMD). In these patients, upper airway obstruction under NIV may compromise efficacy and adherence. We aim to describe a novel pattern of expiratory obstructive events occurring during nocturnal barometric NIV.

Methods: We retrospectively included all patients with DMD who underwent full-night polygraphy during NIV as part of their usual follow-up between May 2018 and July 2019.

Results: We provide a step-by-step description of this previously undescribed pattern of obstruction. Expiratory obstructions lead to end-inspiratory breath-holding and impossibility to take another inspiratory breath with a barometric mode until expiration occurs. These events were observed in 4 (36%) of 11 DMD patients under barometric NIV.

Conclusion: Expiratory obstructions may be common in DMD patients receiving NIV and should be sought out routinely. This previously undescribed variant of obstructive event must be identified.

Keywords: Duchenne muscular dystrophy; neuromuscular diseases; non-invasive ventilation; patient–ventilator asynchrony; sleep apnea.

Figure 1.

Successive complete obstructions beginning at exhalation with ineffective insufflations and air stacking (without leaks). Legend: The tracings are presented in the following order, from top to bottom: oxygen saturation (SpO₂), pressure, flow, respiratory inductive plethysmography (RIP) flow, thoracic movements, abdominal movements, heart rate, finger plethysmography (Pleth), and activity. Pressure and flow were measured with an external pressure sensor and with an external pneumotachograph. AR means air retention; the vertical black arrows point to ineffective insufflations and the vertical white arrows point to partially effective insufflations; the horizontal white arrows indicate expiratory obstructions. [0] appropriate patient–ventilator interaction: pressure increase is associated with adapted flow wave and synchronous thoraco-abdominal movements at both inhalation and exhalation; [1] expiratory obstruction: at the end of an effective insufflation, expiratory obstruction occurs (no significant exhalation observed before the next cycle on the flow, RIP flow, or thoraco-abdominal belts); [2] air stacking: complete (both inspiratory and expiratory) upper airway obstruction with three subsequent ineffective insufflations while the patient remained above the relaxed volume. We must underline that independently of the presence or not of upper airway obstruction, with a pressure mode, additional lung insufflation above the previous insufflation is not possible when reproducing the same inspiratory pressure according to the pressure–volume relationship; [3] apnea resolution: obstruction release begin with a tidal expiration characterized by a return to the relaxed volume as observed on the respiratory inductive plethysmography and flow signals.

Figure 2.

Brief and prolonged expiratory obstructions leading to ineffective and partially effective insufflations and leaks. Legend: The tracings are presented in the following order, from top to bottom: oxygen saturation (SpO ₂ ), pressure, flow, respiratory inductive plethysmography (RIP) flow, thoracic movements, abdominal movements, heart rate, finger plethysmography (Pleth), and activity. Pressure and flow were measured with an external pressure sensor and with an external pneumotachograph. AR means air retention; the vertical black arrows point to ineffective insufflations and the vertical white arrows point to partially effective insufflations; the horizontal white arrows indicate expiratory obstructions. The presence of inspiratory flow during AR periods suggests occurrence of leaks due to the remaining inflation observed on the thoracic and abdominal belts (see Figure 3). * Detailed analysis provided in Figure 3.

Figure 3.

Step-by-step analysis of expiratory obstruction under non-invasive ventilation. AR means air retention; the vertical black arrows point to ineffective insufflations; the horizontal white arrows indicate expiratory obstructions. [0] appropriate patient–ventilator interaction: pressure increase is associated with adapted flow wave and synchronous thoraco-abdominal movements at both inhalation and exhalation; [1] expiratory obstruction: at the end of an effective insufflation, expiratory obstruction occurred (no significant exhalation observed before the next cycle on the flow, RIP flow, or thoraco-abdominal belts); [2] ineffective insufflation with leaks: pressure delivery did not allow additional inflation above the previous inflation (see the RIP signals), independently of the presence or not of upper airway obstruction, according to the pressure–volume relationship; [3] apnea resolution: obstruction release begin with a tidal expiration characterized by a return to the relaxed volume; [4] return to appropriate patient–ventilator interaction. RIP: respiratory inductive plethysmography.